As transistor dimensions continue to shrink in order to increase density and performance, existing device structures and materials are reaching the threshold for many desirable device characteristics. To this end, new materials for existing device structures and novel transistor structures are being explored.
In recent years, III-V compound semiconductors, such as indium arsenide (InAs), gallium arsenide (GaAs), and their alloy indium gallium arsenide (InGaAs), have become materials of interest for the future active channel materials of metal-oxide-semiconductor field-effect transistors (MOSFETs) and as materials for transistors with nanowire (NW) channels.
III-V compound semiconductors are drawing interest because of their superior electron mobilities. However, since the device processing requirements are significantly different from elemental semiconductors such as silicon (Si), III-V compound semiconductors impose a major challenge on nanoscale III-V device fabrication. Among the many challenges, controlling the post-growth dopant profiles in III-V compound semiconductors deterministically has not been well addressed. In the Si industry, ion implantation has been the dominant doping technique for decades. This process, however, presents problems for compound semiconductors, which consist of two or more chemically and electronically nonequivalent lattice sites. Specifically, the stoichiometry can be altered and difficult to recover from implantation induced crystal damage. The residual damage can lead to higher junction leakage and lower dopant activation in compound semiconductors.
For example, much research has been devoted to transistors with nanowire (NW) channels due to their excellent electrostatic properties. Because of its high electron mobility and ease of nanoscale, metal ohmic contact formation to the conduction band via solid source reactions, InAs is emerging as a promising semiconductor for NW devices. However, there remain many challenges to be addressed with InAs NW device fabrication. Specifically, one fabrication issue that requires attention is the dopant profiling of InAs NWs. P-type doping of InAs NWs is particularly challenging given the surface electron-rich layer that causes the surface Fermi level to be pinned in the conduction band for an undoped NW. Although techniques such as in-situ doping during the growth have been previously reported for NWs, post-growth patterned doping is desired for most device fabrication schemes. As with other compound semiconductors, conventional ion-implantation techniques are not compatible with nanoscale InAs semiconductors due to the severe crystal damage induced during the implantation process resulting in In atom clustering, which cannot be fixed by a subsequent annealing process.
Accordingly, there continues to be a need in the art for techniques to control the post-growth dopant profiles in III-V compound semiconductors.